Messages in this thread | | | Date | Sun, 26 Aug 2012 10:40:37 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH v9 0/5] make balloon pages movable by compaction |
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On 08/26/2012 03:58 AM, Michael S. Tsirkin wrote: > On Sat, Aug 25, 2012 at 02:24:55AM -0300, Rafael Aquini wrote: >> Memory fragmentation introduced by ballooning might reduce significantly >> the number of 2MB contiguous memory blocks that can be used within a guest, >> thus imposing performance penalties associated with the reduced number of >> transparent huge pages that could be used by the guest workload. >> >> This patch-set follows the main idea discussed at 2012 LSFMMS session: >> "Ballooning for transparent huge pages" -- http://lwn.net/Articles/490114/ >> to introduce the required changes to the virtio_balloon driver, as well as >> the changes to the core compaction & migration bits, in order to make those >> subsystems aware of ballooned pages and allow memory balloon pages become >> movable within a guest, thus avoiding the aforementioned fragmentation issue > > Meta-question: are there any numbers showing gain from this patchset? > > The reason I ask, on migration we notify host about each page > individually. If this is rare maybe the patchset does not help much. > If this is common we would be better off building up a list of multiple > pages and passing them in one go.
The gain is in getting a better THP allocation rate inside the guest, allowing applications to run faster.
The rarer it is for this code to run, the better - it means we are getting the benefits without the overhead :)
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